Reduction of carbonyl compounds is a very important technology in various fields, inclusive of the production of medicinal compounds and agrochemicals, and various methods have been utilized to answer respective specific purposes. Among them, the technology of converting optically active .alpha.-aminoketone derivatives to .alpha.-aminoalcohol derivatives by stereoselective reduction is required to be high in operability and efficient for industrialization since such .alpha.-aminoalcohol derivatives having an erythro configuration are important as intermediates of anti-HIV drugs, among others.
The "erythro" form means an isomer in which the amino group and hydroxy group bound to the adjacent carbon atoms have the relative configuration shown below. In the following formula, Z.sub.1 and Z.sub.2 represent the remaining chemical structure moieties. ##STR2##
A prior art technology for reducing .alpha.-aminoketone derivatives comprises, for example, reducing them with diisobutylaluminum hydride (DIBAH), sodium borohydride, lithium tri-secondary-butylborohydride (L-Selectride) or the like at -78.degree. C. [Tetrahedron Letters, 36, 5453 (1995)].
The reduction technology using DIBAH is excellent in reactivity and economy and is a very useful method from the( industrial viewpoint. This method is used in reducing, for example, .alpha.-aminochloroketone derivatives derived from leucine. When said .alpha.-aminochloroketone derivatives are reduced with DIBAH at -78.degree. C., the erythro forms can be obtained preferentially with a diastereomer excess of about 75%.
However, this method requires an extremely low temperature of -78.degree. C. for achieving high selectivity.
In Japanese Kokai Publication Hei-8-99959, a technology is disclosed which uses an aluminum trialkoxide as the reducing agent.
However, the technology disclosed in the above publication requires heating at a temperature not lower than 50.degree. C. to raise the rate of reaction although the stereoselectivity is high. Thus, said technology still has problems to be solved; for instance, it is not suited for reducing thermally unstable substrates. Therefore, a practical technology has been demanded by which carbonyl compounds, in particular optically active .alpha.-aminoketone derivatives can be converted to erythro-form .alpha.-aminoalcohol derivatives by stereoselective reduction under mild conditions.